/*
 * kqueue是在UNIX上比较高效的***IO复用技术***
 * 所谓的IO复用，多路连接复用一个IO线程
 * 常见的IO复用技术有select, poll,
 * epoll以及kqueue等等。其中epoll为Linux独占，而kqueue则在许多UNIX系统上存在，包括OS
 * X
 *
 * uloop - event loop implementation
 *
 * Copyright (C) 2010-2016 Felix Fietkau <nbd@openwrt.org>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
static int uloop_init_pollfd(void) {
  struct timespec timeout = {0, 0};
  struct kevent ev = {};

  if (poll_fd >= 0)
    return 0;

  poll_fd = kqueue();
  if (poll_fd < 0)
    return -1;

  EV_SET(&ev, SIGCHLD, EVFILT_SIGNAL, EV_ADD, 0, 0, 0);
  kevent(poll_fd, &ev, 1, NULL, 0, &timeout);

  return 0;
}

static uint16_t get_flags(unsigned int flags, unsigned int mask) {
  uint16_t kflags = 0;

  if (!(flags & mask))
    return EV_DELETE;

  kflags = EV_ADD;
  if (flags & ULOOP_EDGE_TRIGGER)
    kflags |= EV_CLEAR;

  return kflags;
}

static struct kevent events[ULOOP_MAX_EVENTS];

static int register_kevent(struct uloop_fd *fd, unsigned int flags) {
  struct timespec timeout = {0, 0};
  struct kevent ev[2];
  int nev = 0;
  unsigned int fl = 0;
  unsigned int changed;
  uint16_t kflags;

  if (flags & ULOOP_EDGE_DEFER)
    flags &= ~ULOOP_EDGE_TRIGGER;

  changed = flags ^ fd->flags;
  if (changed & ULOOP_EDGE_TRIGGER)
    changed |= flags;

  if (changed & ULOOP_READ) {
    kflags = get_flags(flags, ULOOP_READ);
    EV_SET(&ev[nev++], fd->fd, EVFILT_READ, kflags, 0, 0, fd);
  }

  if (changed & ULOOP_WRITE) {
    kflags = get_flags(flags, ULOOP_WRITE);
    EV_SET(&ev[nev++], fd->fd, EVFILT_WRITE, kflags, 0, 0, fd);
  }

  if (!flags)
    fl |= EV_DELETE;

  fd->flags = flags;
  if (kevent(poll_fd, ev, nev, NULL, fl, &timeout) == -1)
    return -1;

  return 0;
}

static int register_poll(struct uloop_fd *fd, unsigned int flags) {
  if (flags & ULOOP_EDGE_TRIGGER)
    flags |= ULOOP_EDGE_DEFER;
  else
    flags &= ~ULOOP_EDGE_DEFER;

  return register_kevent(fd, flags);
}

static int __uloop_fd_delete(struct uloop_fd *fd) {
  return register_poll(fd, 0);
}

static int uloop_fetch_events(int timeout) {
  struct timespec ts;
  int nfds, n;

  if (timeout >= 0) {
    ts.tv_sec = timeout / 1000;
    ts.tv_nsec = (timeout % 1000) * 1000000;
  }

  nfds = kevent(poll_fd, NULL, 0, events, ARRAY_SIZE(events),
                timeout >= 0 ? &ts : NULL);
  for (n = 0; n < nfds; n++) {
    struct uloop_fd_event *cur = &cur_fds[n];
    struct uloop_fd *u = events[n].udata;
    unsigned int ev = 0;

    cur->fd = u;
    if (!u)
      continue;

    if (events[n].flags & EV_ERROR) {
      u->error = true;
      if (!(u->flags & ULOOP_ERROR_CB))
        uloop_fd_delete(u);
    }

    if (events[n].filter == EVFILT_READ)
      ev |= ULOOP_READ;
    else if (events[n].filter == EVFILT_WRITE)
      ev |= ULOOP_WRITE;

    if (events[n].flags & EV_EOF)
      u->eof = true;
    else if (!ev)
      cur->fd = NULL;

    cur->events = ev;
    if (u->flags & ULOOP_EDGE_DEFER) {
      u->flags &= ~ULOOP_EDGE_DEFER;
      u->flags |= ULOOP_EDGE_TRIGGER;
      register_kevent(u, u->flags);
    }
  }
  return nfds;
}
